Ovarian cancer is a case whose number is the second highest in malignant tumors of female genitalia, and has the highest lethality. This mostly occurs in premenopausal or postmenopausal women. Only in the U.S., annually 26,000 people are newly diagnosed to suffer from ovarian cancer, and 16,000 patients are deceased (in 2004). Five year survival rates for classified stages are 90% for stage I, 70% for stage II, 25% for stage III, and 10% for stage IV, and prognosis of stage III or later is very bad. Therefore, early diagnosis would be the most important issue for improving the long term survival rate. However, most of ovarian cancers in early stage are silent, and a noninvasive definitive diagnosis method has not been established. From these facts, there is rarely the case that ovarian cancer is diagnosed in early stage and completely cured. Therefore, there is a strong need for a tumor marker available for early diagnosis.
The term “tumor marker” refers to a biological molecule (concretely a protein) that is specifically produced by a tumor, and is generally used in the concept of diagnosing presence or absence of a tumor by detection or quantification in bodily fluids (mainly in blood).
As an ovarian cancer marker that is widely used at present in clinical practice, CA125 can be recited first. This marker shows a high positive rate in a malignant tumor, and has been actually used for several tens of years. On the contrary, however, the marker shows a low positive rate and too poor specificity in early stage ovarian cancer. Therefore, it has a drawback that it can not be used in early diagnosis. This is described in MacDonald et al., 1999.
Later, Zhang et al. proposed a method of early diagnosis of ovarian cancer by identifying three kinds of tumor markers from serum of patients suffering from ovarian cancer using a technique called SELDI-TOF-MS combining a surface processing technique and mass spectrometry, and diagnosing the cancer based on the combination of these tumor markers and CA125 (Zhang et al., 2004) (Open Patent Publication No. 2006-512586). However, as described in Nature, 2004, there is an opinion that the methodology lacks a scientific basis. For this reason, this method has not been brought into practical use yet.
On the other hand, Hee Jung An et al., 2006 describes development of a tumor marker taking the difference between tissue-types of epithelial ovarian cancer into account.    Patent Document 1: Open Patent Publication No. 2006-512586    Non Patent Document 1: MacDonald N D, Jacobs I J. Is there a place for screening in ovarian cancer? European journal of obstetrics, gynecology, and reproductive biology 1999; 82(2): 155-7.    Non Patent Document 2: Zhang Z, Bast R C, Jr., Yu Y, et al. Three biomarkers identified from serum proteomic analysis for the detection of early stage ovarian cancer. Cancer research 2004; 64(16):5882-90.    Non Patent Document 3: Check E. Proteomics and cancer: running before we can walk? Nature 2004; 429(6991):496-7.    Non Patent Document 4: An H J, Kim D S, Park Y K, et al. Comparative proteomics of ovarian epithelial tumors. Journal of proteome research 2006; 5(5):1082-90.